1. Field of the Invention
This invention relates generally to micro-scale chemical mixing devices and, more particularly, to a micro-scale device including a mixing reactor that uses non-pressurized liquid chemical with no moving parts.
2. General Background and State of the Art
Micro-Electro-Mechanical Systems (MEMS) is the integration of mechanical elements, sensors, actuators, and electronics on a common silicon substrate through the utilization of microfabrication technology. While the electronics are fabricated using integrated circuit (IC) process sequences, the micromechanical components are fabricated using compatible “micromachining” processes that selectively etch away parts of the silicon wafer or add new structural layers to form the mechanical and electromechanical devices.
MEMS brings together silicon-based microelectronics with micro-machining technology, thereby, making possible the realization of complete systems-on-a-chip. MEMS also uses silicon-based materials because silicon possesses excellent materials properties. For example, silicon has greater strength-to-weight ratio than other engineering materials. Hence, silicon can be used in high-performance mechanical applications. However, MEMS may also encompass any other micro-machining materials.
A typical MEMS includes: 1) microsensors; 2) microactuators; 3) microelectronics; and 4) microstructures. For example, in its most basic form, micro-sensors gather physical information from the environment through measuring mechanical, thermal, biological, chemical, optical, and magnetic phenomena. The microelectronics process the information derived from the micro-sensors and through some decision making capability direct the micro-actuators to respond by moving, positioning, regulating, pumping, and filtering. Hence, controlling the environment for some desired outcome or purpose. Since MEMS devices maybe manufactured using batch fabrication techniques, many levels of functionality, reliability, and sophistication can be placed on a small silicon chip at a relatively low cost.
In short, MEMS is an enabling technology allowing a new way of making complex electromechanical systems using batch fabrication techniques; similar to the way integrated circuits are made.
MEMS manufacturing technology has at least two distinct advantages. First, MEMS is an extremely diverse technology that potentially could significantly impact many categories of commercial and military products. Already, MEMS is used for many products and methods ranging, for instance, from in-dwelling blood pressure monitoring to active suspension systems for automobiles. The nature of MEMS technology and its diversity of useful applications makes it potentially a far more pervasive technology than even integrated circuit microchips. Secondly, MEMS blurs the distinction between complex mechanical systems and integrated circuit electronics. Typically, sensors and actuators are the most costly and unreliable part of a macro-scale sensory-actuator-electronics system. In contrast, MEMS technology allows complex electromechanical systems to be manufactured using batch fabrication techniques, which reduces the cost and increases the reliability of the sensors and actuators.
MEMS is based on a manufacturing technology that has roots in microelectronics, however MEMS is now intimately integrated into macro devices and systems. Thus, MEMS can be applied where size, weight and power must decrease while functionality increases, and at the same time be cost effective.
For example, MEMS accelerometers are quickly replacing conventional accelerometers for crash air-bag deployment systems in automobiles. The conventional approach uses several bulky accelerometers made of discrete components mounted in the front of the car with separate electronics near the air-bag. MEMS has made it possible to integrate onto a single silicon chip the accelerometer and electronics at a reduced cost when compared to the conventional accelerometers. Also, the MEMS accelerometers are much smaller, more functional, lighter, more reliable.
Another application of MEMS technologies is in the area of integrated micro-power generation systems, or MPG. For example, chemicals typically used in MPG systems are high in energy density in comparison with batteries (i.e. rechargeable battery, ˜150 Whr/kg whereas diesel chemical, ˜12,000 Whr/kg). Also, as discussed above, advantages of using MEMS to fabricate MPG include integration of micro-sensors and micro-actuators, complex fluidic system designs using etching and material deposition, and enhance heat transport.
Typically, thermal power generation systems consist of a chemicals injected into the combustor to create heat energy, and a converter that converts the heat energy into electrical energy, or via kinetic energy. Power generation on the micro and nano-scale level is being developed as a means to optimize chemical usage (increase functionality), while minimizing the size of such power producing devices. Standard mechanical combustion devices contain many other large moving parts in addition to a combustion chamber including valves, pressure tanks and/or pumps and devices to mix and ignite the chemical and oxidize it. Thus, with traditional components, standard combustion devices can be large (i.e. on the order of centimeter to meter scale) and heavy, and consequently are not useful as portable, high energy power sources. Thus, smaller and simpler devices are desirable as compact and efficient power sources.
Another problem with traditional combustion devices is that chemical needs to be converted from a liquid state to gaseous state. However, direct injection of liquid chemicals are disadvantageous because they may clog or plug up the internal volume of the combustion device and its components. Alternatively, gaseous chemical injections do not clog or plug up the combustion device. Thus, the liquid chemicals that are used in traditional combustion devices may ultimately impair the longevity and efficiency of MPGs. Therefore, different methods of chemical injection must be devised for the MPGs.
However, one persistent problem in MGPs is the fact that mixing of fluids in the micro-domains is not as effective as in macro-domains. Furthermore, gases mix at orders of magnitudes faster than liquids. So, ideally mixing should be performed at gaseous phase whenever possible.
Therefore, now more than ever, there is a need for research development of useful, efficient and portable nano- and micro-scale chemical mixing devices. Ideally, such devices will employ chemical combustion, heat transfer, fluid dynamics and acoustics.